Buggy code:
public class CSharp extends org . apache . tools . ant . taskdefs . MatchingTask { protected static final String csc_exe_name = "csc" ; protected static final String csc_file_ext = "cs" ; protected static final String csc_file_pattern = "**//*." + ( CSharp . csc_file_ext ) ; protected static final String DEFAULT_REFERENCE_LIST = "Accessibility.dll;" + ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( "cscompmgd.dll;" + "CustomMarshalers.dll;" ) + "IEExecRemote.dll;" ) + "IEHost.dll;" ) + "IIEHost.dll;" ) + "ISymWrapper.dll;" ) + "Microsoft.JScript.dll;" ) + "Microsoft.VisualBasic.dll;" ) + "Microsoft.VisualC.dll;" ) + "Microsoft.Vsa.dll;" ) + "Mscorcfg.dll;" ) + "RegCode.dll;" ) + "System.Configuration.Install.dll;" ) + "System.Data.dll;" ) + "System.Design.dll;" ) + "System.DirectoryServices.dll;" ) + "System.EnterpriseServices.dll;" ) + "System.dll;" ) + "System.Drawing.Design.dll;" ) + "System.Drawing.dll;" ) + "System.Management.dll;" ) + "System.Messaging.dll;" ) + "System.Runtime.Remoting.dll;" ) + "System.Runtime.Serialization.Formatters.Soap.dll;" ) + "System.Security.dll;" ) + "System.ServiceProcess.dll;" ) + "System.Web.dll;" ) + "System.Web.RegularExpressions.dll;" ) + "System.Web.Services.dll;" ) + "System.Windows.Forms.dll;" ) + "System.XML.dll;" ) ; protected boolean _utf8output = false ; protected boolean _noconfig = false ; protected boolean _fullpaths = false ; protected boolean _debug ; protected File _docFile ; protected String _extraOptions ; protected boolean _failOnError ; protected boolean _includeDefaultReferences ; protected boolean _incremental ; protected String _mainClass ; protected boolean _optimize ; protected File _outputFile ; protected Path _referenceFiles ; protected String _references ; protected String _targetType ; protected boolean _unsafe ; protected File _win32icon ; protected File _win32res ; String _additionalModules ; String _definitions ; private File _destDir ; private File _srcDir ; private int _warnLevel ; public CSharp ( ) throws TaskException { } public void setAdditionalModules ( String params ) { } public void setDebug ( boolean f ) { } public void setDefinitions ( String params ) { } public void setDestDir ( File dirName ) { } public void setDocFile ( File f ) { } public void setExtraOptions ( String extraOptions ) { } public void setFailOnError ( boolean b ) { } public void setFullPaths ( boolean enabled ) { } public void setIncludeDefaultReferences ( boolean f ) { } public void setIncremental ( boolean f ) { } public void setMainClass ( String mainClass ) { } public void setOptimize ( boolean f ) { } public void setOutputFile ( File params ) { } public void setReferenceFiles ( Path path ) throws TaskException { if ( ( _referenceFiles ) == null ) <START_BUG> _referenceFiles = new Path ( this . project ) ; <END_BUG> _referenceFiles . append ( path ) ; } public void setReferences ( String s ) { } public void setSrcDir ( File srcDirName ) { } public void setTargetType ( String targetType ) throws TaskException { } public void setUnsafe ( boolean unsafe ) { } public void setUtf8Output ( boolean enabled ) { } public void setWarnLevel ( int warnLevel ) { } public void setWin32Icon ( File fileName ) { } public void setWin32Res ( File fileName ) { } public boolean getDebug ( ) { } public String getExtraOptions ( ) { } public boolean getFailFailOnError ( ) { } public boolean getIncludeDefaultReferences ( ) { } public boolean getIncremental ( ) { } public String getMainClass ( ) { } public boolean getOptimize ( ) { } public String getTargetType ( ) { } public boolean getUnsafe ( ) { } public int getWarnLevel ( ) { } public void Clear ( ) { } public void execute ( ) throws TaskException { } protected void setNoConfig ( boolean enabled ) { } protected String getAdditionalModulesParameter ( ) { } protected String getDebugParameter ( ) { } protected String getDefaultReferenceParameter ( ) { } protected String getDefinitionsParameter ( ) { } protected String getDocFileParameter ( ) { } protected String getExtraOptionsParameter ( ) { } protected String getFullPathsParameter ( ) { } protected String getIncludeDefaultReferencesParameter ( ) { } protected String getIncrementalParameter ( ) { } protected String getMainClassParameter ( ) { } protected String getNoConfigParameter ( ) { } protected String getOptimizeParameter ( ) { } protected String getOutputFileParameter ( ) { } protected String getReferenceFilesParameter ( ) { } protected String getReferencesParameter ( ) { } protected String getTargetTypeParameter ( ) { } protected String getUnsafeParameter ( ) { } protected String getUtf8OutpuParameter ( ) { } protected String getWarnLevelParameter ( ) { } protected String getWin32IconParameter ( ) { } protected String getWin32ResParameter ( ) { } protected boolean notEmpty ( String s ) { } }

Fix:
_referenceFiles = new Path ( this . getProject ( ) ) ;